This invention concerns erythorbic and ascorbic acids. More specifically, it concerns the preparation of fatty acid monoesters of these compounds.
Erythorbic and ascorbic acids, because of their nontoxic nature and strong reducing power, are commonly used as antioxidants in food. In exploiting this antioxidant property with foods of high fat content, erythorbic acid and ascorbic acid 6-fatty acid esters, which possess a higher fat solubility with retained reducing power, are preferred. These esters are additionally used as emulsion stabilizers in food preparations, and the ascorbic acid ester may also serve as a source of Vitamin C.
These fatty acid monoesters of erythorbic and ascorbic acids, such as erythorbic acid 6-palmitate, are currently prepared utilizing concentrated sulfuric acid as catalyst and solvent. In such preparations, one of the reactants is routinely used in excess. The fatty acid, being the less expensive ingredient, is normally selected, although preparations in which the fatty acid is the limiting ingredient have also been reported (Oil and Soap, 20, page 224, 1943). In either case, the yield to monoester is only about 50 percent. A further drawback of this system is the difficulty encountered in separating the product from the excess reactant, particularly in the case of excess fatty acid. It is therefore the object of this invention to overcome such difficulties.
While it is known from U.S. Pat. No. 3,551,464 that anhydrous hydrogen fluoride can be employed in the esterification of simple polyols such as glycerol, it was never recognized that this medium would be useful for the esterification of erythorbic or ascorbic acid.